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RLC circuit frequency

  1. Nov 20, 2008 #1
    1. The problem statement, all variables and given/known data

    A RLC circuit has a resonance frequency of 6 KHz. When it is driven by a 8 KHz ac generator, it has an impedance of 1 k W. What are R, L and C in the circuit?

    2. Relevant equations

    3. The attempt at a solution

    the equation for the resonant frequency will be
    fo = 1 / 2 π √(L C)
    the equation for the impedence will be
    Z = √[R2 + (XL - XC)^2]
    where XL = 2 π f L

    XC = 1 / 2 π f C
    f = 8 x 10^3 Hz
    fo = 6 x 10^3 Hz
    Z = 1 x 10^3 Ω

    How am I supposed to solve for the three unkowns(R,L,C) with only two equations? Is there a third relationship for R?
  2. jcsd
  3. Nov 20, 2008 #2


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    Are you sure there is no impedence at resonance given?
  4. Nov 20, 2008 #3
    No impedance at resonance is given. That's what I was thinking...it'll be impossible to solve if you don't have a relation for R.
  5. Nov 20, 2008 #4


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    Gold Member

    Is your circuit series or parallel?
    And what is this: "...it has an impedance of 1 k W"? Do you mean kohm of the circuit or the generator?
  6. Nov 20, 2008 #5


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    I recall a very similar problem but the Impedance at resonance was given:
  7. Nov 20, 2008 #6


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    I think he used the Latinized W instead of Ω.
  8. Nov 20, 2008 #7
    well, the question was given by my professor. I am 100% sure that there is a peice of informaiton missing from the original question.

    BTW, the RLC is connected in series.
  9. Nov 20, 2008 #8
    It turns out that he forgot to say that the phase angle=45 degrees...ugghhhh....It's an easy one now.

    Thanks for the help!
  10. Nov 20, 2008 #9


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    Alrighty then. There's your third equation.

    Good luck.
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